The rose garden moment could never last. The warm coalition glow after David Cameron and Nick Clegg improbably plighted their troth on the lawn at No 10 was bound to cool as the grinding daily realities of government took their toll. 2011 has been a much tougher year for the principal players than was 2010.

Cameron endured the debilitating saga of the phone-hacking scandal, which undermined his judgement. Clegg's hardest blow was sharper, a thrashing in the AV referendum campaign. Both men were complicit in the shambles of NHS reform and much else – while George Osborne saw his hopes of economic recovery dwindle as financial belt-tightening, Britain to the fore, took its toll on western states.

The coming year will take the coalition to the mid-point of the five-year parliament it has promised. How do the main parties renew their sense of purpose and vision while also responding to changing circumstances? To challenges they knew would be difficult, such as job creation amid cuts? And to those they could not have foreseen like the Arab spring – including the Libya campaign – and the riots in English cities?

Cameron is widely mistrusted by his right wing and many activists who wonder what the prime minister really stands for. But Tory troubles are providing no automatic balm to Labour (let alone the Lib Dems, deeply wounded by what many voters saw as their betrayal over student fees). Ed Miliband struggles to assert his authority over his party and develop themes that impress core voters and the elusive middle ground.

At this year's round of political party conferences the Guardian's annual debates will focus on new themes, revised priorities and strategies to reflect a changed political environment. It now invites readers of Comment is free to make their own suggestions, which can be fed into debates on the conference fringe where leading politicians of all parties will participate.

Should the Tories trim their flagship policy as cuts appear to make recovery harder?

Should the Lib Dems stop wasting valuable political capital on divisive constitutional reforms that weaken their hand within the coalition?

Should Labour move leftwards to re-establish its credentials as Britain's radical alternative?

In the thread below, make one brief suggestion for each party's midterm manifesto. Martin Kettle and I will select five of these contributions to take to each of the panel debates. We'll then invite the reader whose idea receives the most interest to write an article for Comment is free, explaining it in more depth.